An OLED device, such as an OLED display, is used in applications such as displays of cellular phones because the OLED device is thin, is excellent in displaying a moving image, and has low power consumption.
A glass substrate is widely used as a substrate of an OLED display. Glass substantially free of an alkali metal oxide, that is, alkali-free glass is used for the glass substrate of this application. When the alkali-free glass is used, a situation in which an alkali ion is diffused in a heat treatment step into a semiconductor substance having been formed into a film can be prevented.